The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface. Question 45Ignoring any attachments between the spinal discs and vertebrae, how would the maximum force of static friction between these anatomical structures compare for a person standing on the surface of the Moon to a person standing on the surface of the Earth?A.It would be 6 times as great.B.It would be approximately equal.C.It would be 1/6 as great.D.It would be 0.

Microgravity results in numerous physiological changes in astronauts. Which of the following is commonly observed in astronauts and cosmonauts? (select all that are correct, even if it is only one answer):Each correct answer will score partial points, each incorrect answer will score an equivalent deductionGroup of answer choicesMaintenance of core and postural muscle with exerciseReduction in plasma volume can results in decrease in diuresisFluid shift to the core and head can result in ‘puffy’ facesThere is an increased risk of kidney stones in astronauts due to bone resorption

Microgravity is a unique environment and many things can happen to the human body. What are ways that microgravity might affect a human organ system? Group of answer choicesLoss of bone densityFluid shiftingChanges in body composition due to altered diet and activityAltered kidney or liver functionAll of the above

Which best describes how astronauts are affected by microgravity?Select one:They are lifted by oxygen in the air.They are not subjected to an atmosphere.They are not subjected to gravity.They are constantly falling toward Earth.

When people have no forces to support their weight, such as astronauts in space, they can feel the sensation of .

Life on earth has evolved with the gravitational force of 1g. Which of the following statements is true in light of this context (select all that are correct).Each correct answer will score partial points, each incorrect answer will score an equivalent deduction.Group of answer choicesThe removal of the gravitational force will result in a fluid shift towards the lower limb and this contributes to the orthostatic intolerance of early astronauts.To overcome the effect of gravity, giraffes have higher mean arterial pressure at the heart (compared to humans) to ensure perfusion of the head.The pull of gravity generates a fluid column within the body with greater volume towards the lowest point closest to earth.The gravitational force provides load on the musculoskeletal system, and the removal of this force leads to bone and muscle loss.